The present invention relates to correction of errors in signals and, in particular, to correction of errors in signals utilizing transmitted error correction information.
When signals are transmitted from a source location to a receiver location, error is introduced into the signals due to many conditions, among which are interference signals, reflections and ghost signals, noise signals and the like, as well as by imperfections in the transmitting and/or receiving apparatus. Such errors occur in video signals as well as in non-video related data signals. Some level of error may be tolerable to a user or viewer of the error-laden received signal, as with the case of occasional xe2x80x9csnowxe2x80x9d or xe2x80x9cconfettixe2x80x9d in an analog television signal, for example, because the analog television signal tends to degrade xe2x80x9cgracefullyxe2x80x9d in the presence of noise and interference, principally due to the viewer""s tolerance of the undesired effect in the picture.
In digital systems, on the other hand, the effects of such noise and interference on a digital signal transmission may be more pronounced, e.g., a sudden complete corruption of digital data or loss of picture, despite the generally superior resistance of digital systems to the effects of noise and interference. A prominent digital television system is the advanced television (ATV) broadcasting protocol established by the Advanced Television Systems Committee (ATSC) in the United States. (See, e.g., xe2x80x9cGuide to the Use of the ATSC Digital Television Standardxe2x80x9d available via the Internet from the ATSC at www.atsc.org/Standards/stan_rps.html and ATV Standard A54 dated Oct. 4, 1995 also available via the Internet from the ATSC at www.atsc.org/Standards/A54/ and from the United States Federal Communication Commission at www.fcc.gov/Bureaus/Engineering_Technology/Documents/atsc/a54/). The ATSC ATV protocol includes a forward error correction protocol designed to provide a level of error correction deemed adequate for normal viewing of broadcast television program material. For example, the expected bit error rate for broadcast signals of about 10xe2x88x924 is correctable to about 10xe2x88x928 by utilizing the error correction system specified by the ATSC ATV protocol.
The ATSC ATV protocol provides an ancillary data channel that may be used to transmit data which may or may not be related to the video and data contained in the principal broadcast signal or principal data channel. Because the ancillary data channel is interleaved with the principal data channel, the capacity of the ancillary data channel varies in inverse relation to the content of the principal data channel. Where the data content of the principal data channel is low such as when there is substantial redundancy in the video content thereof, the number of digital bits required to transmit such video data content is relatively lower, thereby permitting the data content of the ancillary data channel to increase commensurately. Conversely, where the data content of the principal data channel is high such as when there is substantial change and little redundancy in the video content thereof, the number of digital bits required to transmit such video data content is relatively higher, thereby reducing the possible data content of the ancillary data channel commensurately.
While the specified ATSC ATV error correction protocol may be satisfactory for viewing of broadcast video programming, it is not satisfactory for certain other applications requiring much lower bit error rates. Such applications include, for example, high-quality video data storage and retransmission, computer data transmission, and secure data transactions, which typically require bit error rates at a level of about 10xe2x88x9212, which is comparable to the bit error rate obtainable for data read from a CD-ROM. To be advantageous, transmission systems providing such reduced error rates should be compatible with the ATSC transmission specification so that standard receivers capable of receiving and processing the standard ATSC-specified data transmissions are not incapacitated by the presence of an improved error correction signal contained in the ancillary data channel and so that receivers intended for receiving the improved error correction signal contained in the auxiliary data channel will properly receive and process the ATSC standard error correction signal.
Accordingly, there is a need for an error correction arrangement providing improved error correction when received by suitably equipped receivers, without unduly affecting the operation of conventional ATSC standard receivers.
To this end, the error correction arrangement of the present invention comprises an information transmission system comprising a transmitting arrangement encoding the information, a receiving arrangement decoding the information, and a transmission system coupling the transmission arrangement to the receiving arrangement for coupling encoded information thereto.
In accordance with the invention, a transmitting arrangement comprises a first encoder producing first data packets, each first data packet including data bytes representative of the information and first error-correction bytes relating to the data bytes thereof, a second encoder producing at least one additional data packet including second error-correction bytes relating to predetermined data bytes of a predetermined number of the first data packets produced by the first encoder, and a multiplexer combining the first data packets produced by the first encoder and the at least one additional data packet produced by the second encoder.
In accordance with the invention, a receiving arrangement comprises a separator for separating the first data packets from the at least one additional data packet, a first decoder responsive to the first data packets to produce uncorrected data bytes and corrected data bytes thereof responsive to the first error-correction bytes thereof, a second decoder responsive to the second data packets to produce corrected predetermined data bytes representative of the predetermined data bytes responsive to the second error-correction bytes of the second data packets, and a corrector replacing selected ones of the uncorrected data bytes and corrected data bytes with selected ones of the corrected predetermined data bytes to produce the information.
In a method of encoding and decoding information according to the invention encoding the information comprises:
producing first data packets, each first data packet including data bytes representative of the information and first error-correction bytes relating to the data bytes thereof,
producing at least one additional data packet including second error-correction bytes relating to predetermined data bytes of a predetermined number of the first data packets, and
combining the first data packets and the at least one additional data packet; and decoding the information comprises:
separating the first data packets from the at least one additional data packet,
responsive to the first data packets, producing uncorrected data bytes and corrected data bytes thereof responsive to the first error-correction bytes thereof,
responsive to the second data packets, producing corrected predetermined data bytes representative of the predetermined data bytes responsive to the second error-correction bytes of the second data packets, and
replacing selected ones of the uncorrected data bytes and corrected data bytes with selected ones of the corrected predetermined data bytes to produce the information.